The European Commission issued formal objections Friday to Bayer’s planned $66 billion takeover of Monsanto, according to two people briefed on the case, signaling the deal may be blocked unless the German company makes more significant concessions.

The objections from Brussels represent a stark ultimatum for the agrichemical giant, which has spent at least 12 months trying to bring around EU regulators on the politically charged mega-merger.

When announced, Bayer’s tie-up with Monsanto was set to create the world’s largest portfolio of pesticides, but Bayer has already sold off some businesses to allay competition concerns. Monsanto is a bête noire among European environmentalists because of its production of genetically modified crops and the ubiquitous pesticide glyphosate, and many non-governmental organizations are pinning their hopes on European Commissioner for Competition Margrethe Vestager to kill off what has been dubbed by some as the #mergerfromhell.

Given her track record on other tie-ups in the sector, however, it is more likely that she will simply press for divestments. Bayer and Monsanto’s merger is the last of the trio of mega-mergers that have dramatically consolidated the agrichemical industry. Two of the deals — Dow’s tie-up with DuPont and ChemChina’s acquisition of Syngenta — obtained EU clearance at the end of long probes and on the condition they sold off some businesses.

The Commission, which has until March 5 to reach a final decision, has the power to either block mergers or demand divestments by the companies.

As was the case with the inquiry into Dow and DuPont, which merged earlier this year, people following the Bayer case say the Commission is running an extremely wide-reaching investigation and is demanding huge amounts of information.

The objections were issued Friday, according to one of the people briefed. The Commission’s specific concerns remain confidential. The Commission and Monsanto declined to comment.

“We do not comment on rumors,” said Utz Klages, a spokesperson for Bayer.